The invention relates to material level sensors and more particularly to electronic material level sensors using time domain reflectometry (TDR).
Parent application Ser. No. 08/359,090 filed Dec. 19, 1994 describes an electronic material level sensor or "electronic dipstick" based on time domain reflectometry (TDR) of very short electrical pulses. Pulses are propagated along a transmission line or guide wire that is partially immersed in the material being measured; a launcher plate is positioned at the beginning of the guide wire. Reflected pulses are produced at the material interface due to the change in dielectric constant. The time difference of the reflections at the launcher plate and at the material interface are used to determine the material level. Accuracy of about 1% is achieved where the time base accuracy is dependent on RC components. In some cases, however, there is a need for more accurate measurement of material level.
There is also a problem when the reflected pulse returns while the outbound pulse is still being transmitted, i.e. when the reflecting discontinuity is very close to the input or launch end of the transmission line. In these cases it may be necessary to connect the electronics to the transmission line through a cable to sufficiently separate the transmitted and reflected pulses. However, there is a need for a system which does not require a cable wherein the electronics can be connected directly to the launch point of the dipstick.
U.S. Pat. No. 5,345,471 and copending CIP application Ser. No. 08/301,924 filed Sep. 6, 1994, now U.S. Pat No. 5,523,760 which are herein incorporated by reference, describe an ultra-wideband (UWB) receiver which utilizes a strobed input line with a sampler connected to an amplifier. The outputs of two integrating single-ended samplers are input into a differencing amplifier. The samplers integrate, or average, up to 10,000 pulses.
Copending application Ser. No. 08/510,956 (Docket No. IL-9797) filed herewith now U.S. Pat. No. 5,517,198 entitled "Ultra-Wideband Directional Sampler" describes a four port electronic directional coupler which combines a directional coupler with a high speed sampler for use in time domain reflectometry. Two of the ports operate at sub-nanosecond speed, in "real time", and the other two ports operate at a slower millisecond speed, in "equivalent time". A signal flowing inbound to either of the high speed ports is sampled and coupled, in equivalent time, to the adjacent equivalent time port while being isolated from the opposite equivalent time port.
Copending application Ser. No. 08/510,524 (Docket No. IL-9772) filed Aug. 2, 1995 now U.S. Pat. No. 5,563,605 entitled "Precision Digital Pulse Phase Generator" describes a high accuracy time base that is referenced to a quartz crystal.